1. Technical Field
The present disclosure relates to a variable-capacitance electronic device and to a microelectromechanical device incorporating such electronic device.
2. Description of the Related Art
As is known, the use of microelectromechanical systems (MEMS) is encountering an increasingly widespread use in various sectors of technology and has yielded encouraging results especially in the production of inertial sensors, microintegrated gyroscopes, and electromechanical oscillators for a wide range of applications.
MEMS of this type are usually based on microelectromechanical structures comprising at least one mass, which is connected to a fixed body (stator) by springs and is movable with respect to the stator according to pre-set degrees of freedom. The movable mass and the stator are capacitively coupled through a plurality of respective electrodes, mutually facing so as to form capacitors. The movement of the movable mass with respect to the stator, for example on account of an external load, changes the capacitance of the capacitors. From this change it is possible to trace back to the relative displacement of the movable mass with respect to the fixed body and hence to the force applied. Vice versa, by supplying appropriate biasing voltages, it is possible to apply an electrostatic force to the movable mass to set it in motion. In addition, in order to provide electromechanical oscillators, the frequency response of the inertial MEMS structures is exploited, which is typically of a second-order low-pass type, with a resonance frequency.
MEMS gyroscopes have a more complex electromechanical structure. In these devices, a first movable mass, or driving mass, is set in oscillation according to an axis at a pre-set frequency and drives in the oscillatory motion a second mass, or detection mass, which is constrained to the driving mass so as to have a relative degree of freedom. When the gyroscope undergoes a rotation about a given axis with an angular velocity, the detection mass is subject to a Coriolis force as a result of the driving action and moves in accordance with the relative degree of freedom. The displacements of the detection mass can be detected and transduced into electrical signals, which are amplitude-modulated proportionally to the angular velocity, with a carrier at the frequency of oscillation of the driving mass. The use of a demodulator makes it possible to obtain the modulating signal and hence to trace back to the instantaneous angular velocity.
In many cases, the acceleration signal that carries information on the instantaneous angular velocity contains also spurious components that are not determined by the Coriolis acceleration and hence present as disturbance. Sometimes, the spurious components depend upon inevitable constructional imperfections of the MEMS part, due to the limits of precision and to the dispersion of the manufacturing processes. For example, the oscillation axis of the driving mass could, on account of a fault in making the constraints, be misaligned with respect to the direction theoretically expected. This type of defect commonly causes a quadrature-signal component, which adds to the useful signal due to the rotation of the gyroscope. Obviously, the consequences are a degraded signal-to-noise ratio and altered dynamics of a reading interface, at the expense of the signal to be read, to an extent that depends on a degree of the defects.